1. Field of the Invention
This invention relates to the deposition of semiconductor materials and, in particular, the deposition of semiconductor materials utilizing organometallic compounds.
2. Art Background
Recently, the use of II-VI semiconductor materials in infrared detection devices, such as devices utilized for observing objects in low light surroundings, has generated substantial interest. Additional interest has been generated by the contemplated use of these material in applications such as detectors and lasers for optical fiber communications.
For any of these uses, the II-VI material must, during the fabrication process, be deposited on a mechanically stable structure, i.e., a substrate. This deposition of semiconductor materials such as II-VI semiconductor materials, e.g., cadmium telluride, mercury telluride, cadmium sulfide, zinc selenide and mercury cadmium telluride, is, in one method, accomplished by a metal-organic chemical vapor deposition procedure (MOCVD). In this procedure a deposition vapor flow containing at least one organometallic compound is established, and deposition is induced by interaction with the heated substrate. For example, cadmium telluride has been deposited by passing a combination of dimethylcadmium and either dimethyltelluride or diethyltelluride over a substrate heated to a temperature typically in the range 340.degree. C. to 420.degree. C. Similarly, various procedures have been developed for the deposition of cadmium mercury telluride utilizing precursors such as elemental mercury, dimethylcadmium, and diethyltelluride.
To fabricate many useful devices, it is necessary to deposit sequentially a multiplicity of compositionally differing layers. In such deposition procedures, the precursor material for depositing the first layer is introduced and after deposition of sufficient material, this precursor is changed to induce the formation of subsequent overlying layers. Frequently, e.g., for mercury entities, interdiffusion occurs between adjacent layers or between the substrate and its overlying layer inducing degradation in device performance.
The use of low temperature deposition prevents interdiffusion and also limits the amount of volatile materials escaping from the layer being deposited. This latter effect is quite significant for deposited layers containing entities such as mercury with high vapor pressures. For such materials, high precursor partial pressures are required to limit the extent of volatilization and thus to limit, in turn, control of device properties. However, use of high precursor concentrations is inconvenient because, for materials such as elemental mercury, the entire gas flow pathway must be heated to prevent condensation of the precursor before it reaches the substrate. Additionally, for materials such as dimethylmercury use of high concentration is not economic.
Various expedients have been utilized in an attempt to lower the deposition temperature and thus lower the extent of interdiffusion and volatilization. For example, the precursor material at the substrate has been irradiated with ultraviolet light, i.e., light of wavelength 194 to 260 nm. Although this procedure has proven useful for depositing II-VI materials at temperatures as low as 200.degree. C., the introduction of light through the deposition apparatus from an external source introduces difficulties. Exemplary of such difficulties is the frequent maintenance required to remove internal deposits of opaque matter from the window utilized to introduce the light. Thus, expedient processes for low temperature deposition of materials, such as II-VI semiconductor materials, are still quite desirable.